Presses of the subject character conventionally include a pair of die sections, and a ram or other suitable means for propelling one of the die sections against the other so as to form a workpiece positioned therebetween. A die cushion is coupled to one of the die sections for absorbing the force of die engagement. Typically, the die cushion has included a multiplicity of coil springs that engage the opposing die pad for resiliently absorbing the forces of die engagement. It has heretofore been proposed to replace such coil springs with gas spring cylinders coupled to a die cushion manifold. The manifold supplies gas under pressure to the cylinders for resiliently absorbing the force of die engagement. It is important in gas cylinder die cushions of the described character that manifold gas pressure be maintained within a range determined by press operation. If the gas pressure falls below the minimum desired level, due to cocking of the die pad or gas leakage for other reasons, not only will the press produce unsatisfactory workpieces, but continued operation could damage the press and result in significant downtime and repair cost.
It is therefore a general object of the present invention to provide a press of the described character that includes facility for monitoring gas pressure within the die cushion manifold and controlling operation of the press as a function of manifold gas pressure. A more specific object of the present invention is to provide a press of the described character in which press operation is disabled when die cushion gas pressure is below a preselected or predetermined minimum threshold. Another object of the present invention is to provide a press of the described character that includes facility for operator adjustment of the minimum manifold gas pressure threshold, and/or for automatically feeding gas under pressure to the manifold when manifold pressure is less than the minimum threshold.